Refrigeration systems, and in particular heat pump systems, selectively heat or cool a space to be conditioned and employ positive displacement refrigerant compressors which may take the form of single or multiple reciprocating pistons, multiple intermeshed helical screws, or other forms of rotary compressors such as the rotary sliding vane, and to a very minor degree, a single rotary screw utilizing rotating guide or sealing members. Such systems pick up heat through a closed refrigerant loop external of a space to be conditioned and supply heat thereto through one coil acting as a system evaporator external of the space and through a second coil which releases that heat to the space being conditioned, and functioning as a condenser.
Alternatively, by reversal of refrigerant flow, heat may be absorbed within the space to be conditioned by employing the second coil as the system evaporator and by discharging that heat external of the space by way of the first coil acting as the system condenser. Additionally, waste heat may be removed from the space being conditioned by an additional coil or coils functioning as system evaporators and that energy may be then supplied to the system or stored for some time by means of a heat storage media thermally insulated from the space to be conditioned, although located within that space. Additional thermal energy may be supplied by solar radiation, and while thermal energy may be picked up external of the space to be conditioned within the atmosphere or from the ground itself, present day technology, particularly in heat pump systems, requires, because of the high cost of fuel or electrical energy to operate the system, control measures to permit automatic system operation at highest system efficiency and by utilization of waste heat available to the system, whereby external solar, air or ground energy may be supplied, dependent upon environment conditions on a day to day basis and, in fact, on an hour to hour basis.
The refrigeration systems, particularly heat pump systems, must be designed so that the system is capable of providing the necessary cooling or heating load to the space or spaces to be conditioned throughout the year, and this causes some difficulty, particularly where there is a large seasonal change. Conventionally, temperature sensors are employed to operate solenoid operated control valves, and the conduits or other refrigerant circulation means between the components of the system involve check valves, reversing valves and the like, to permit system change to meet cooling and heating loads for the same areas or spaces to be conditioned and to incorporate within the system the coils such as the outside air coil, storage coil, inside air coil, direct solar energy supply coil, hot water coil, as needs or system efficiency requirements call for their inclusion. Further, because the system requirements fluctuate greatly even from hour to hour in terms of the need for heating, cooling, dissipation or storage of thermal energy, attempts have been made to provide compressors having variable capacity capabilities and operating efficiently regardless of compressor load conditions as well as the capability of permitting intermediate pressure level return of refrigerant vapor or discharge of refrigerant vapor at intermediate pressure levels with respect to full compressor pressure discharge.
Where the compressor is constituted by a multi-cylinder reciprocating piston compressor, and taking for example a compressor comprised of four cylinders, assuming 100% volumetric efficiency under single stage operation equates to four flow units, at 50% volumetric efficiency the single stage operation result is only equivalent to two flow units. At higher system compression ratios, the reciprocating compressor volumetric efficiency drops to a very low value and a reduction to 25% volumetric efficiency under maximum heating conditions is quite common. In such a case, the result is but one flow unit at the higher compression ratios. Further, in achieving improved system efficiency in contrast to compressor efficiency, it is conventional, particularly in heat pump refrigeration systems, to incorporate a subcooler to subcool the liquid refrigerant downstream of that coil within the system constituting the system condenser and prior to feeding of the same to the coil acting as the evaporator for the system. In such cases, a portion of the high pressure liquid refrigerant which is bled from the system and vaporized to further reduce the temperature of that portion of the refrigerant delivered to the coil functioning as the evaporator for the system under a given particular mode, results in the generation of vapor in the subcooler which is at a pressure which is well above the suction pressure of the reciprocating compressor. As a result, returning the subcooler vapor to the suction side of the reciprocating compressor results in expansion of the refrigerant vapor to meet the pressure of the refrigerant vapor entering the compressor from the downstream or discharge side of the evaporator coil and thereby constituting a system loss reducing the efficiency of the heat pump system or other refrigerant system employing the same.
Further, and particularly in refrigeration systems where one of the evaporators functions to maintain a given space such as a refrigerator cooler at a temperature somewhat above freezing while another evaporator coil functions to maintain a completely separate space such as a freezer locker at a temperature well below freezing, the result is the provision of two different vapor return pressure levels for the compressor, with an intermediate pressure level defined by the higher temperature compartment or space, perhaps being somewhat different from the intermediate pressure level of the subcooler vapor return. On the opposite or high pressure side of the system, particularly under heat pump requirements, the space to be conditioned such as the interior of the building may be supplied heat at a low condensing temperature and therefore by a low pressure condenser with the room being heated by a coil operating at approximately 80.degree. F., while a portion of the refrigerant vapor compressed by the compressor may be delivered to a second, high pressure condenser coil acting as a hot water coil within a hot water tank and maintaining the temperature of that hot water at a level of perhaps 120.degree. F. In that case, these condenser coils comprise discharge loads to the compressor which are distinctly different.
Additionally, and also within heat pump systems where during times of intense solar radiation a solar source evaporator coil may function at a much higher temperature than that of an air source coil, both coils may function to deliver or supply heat to the heat pump system, but with the evaporator return vapors at different low side pressures.
Finally, in the refrigeration system, whether it be a heat pump system or a commercial locker or cold storage plant or the like, there are times when the heating and/or cooling loads are relatively high as against times when they are relatively low. During the winter months, particularly in the northeast states, where the refrigeration system comprises a heat pump system, there are extremely high heating loads and conversely during the summer months there are fairly high refrigeration or cooling loads. To the contrary, during the spring and fall, or even over a 24 hour period particularly during times of intense solar radiation, the compressor may be required only to operate at 1/4 its maximum load and the system necessarily must automatically adjust the capacity control of the compressor to system needs regardless of whether the compressor constitutes a reciprocating compressor or a rotary compressor.
It is, therefore, a primary object of the present invention to provide an improved refrigeration system employing a multiple cylinder reciprocating compressor which automatically meets system requirements in terms of load on the compressor while varying pressure level supplies and permitting varying pressure level returns at the low side of the system.
It is a further object of this invention to provide an improved air source heat pump system employing a multiple cylinder reciprocating piston compressor operating at five pressure levels, in which the cylinders are automatically staged and which automatically connect to evaporator coil returns dependent upon those coil operating conditions, while maintaining load reversal on the wrist pins of the reciprocating compressor pistons and connecting rod assemblies dependent upon the highest pressure level of the various refrigerant returns to the compressor.
It is a further object of the present invention to provide an improved refrigeration system employing a modular multiple cylinder reciprocating compressor within the system in the absence of reversing valves and their attendant controls and wherein the compressor may be employed in conjunction with discharge, suction, liquid feed, and liquid drain manifolds common to a plurality of coils which may be connected selectively to either the high side or low side of the compressor and at different pressure levels.